Air lock in raw water pump

[Rik-lu]

Originally Posted by Terra Nova

If the 6 others who have the same problem were all in your marina, I think you'd have an argument.

if You google "Air lock in raw water pump" You see this problem is quite common....

[Stu Jackson]

Originally Posted by Rik-lu

if You google "Air lock in raw water pump" You see this problem is quite common....

Good idea.

The only reason that this occurs has to be an air leak, most likely from the top of the strainer, but could be anywhere in the hose system or the pump faceplate.

This is pretty simple hydronics.

[Terra Nova]

Of all those who reported "air lock" as the problem, how many had
a) a bad pump
b) a bad installation
c) some other problem?

[Rik-lu]

I had the problem for 4 years, remarked first time when the engine had run only 100 hours.

I even had not only to fill the filter with water (with the seacock closed) but also had to drain the seawaterpump by loosening the 4 little screws. I mounted a speedseal to be able to drain the watersystem faster and I'm happy to have that.
Always had a couple of full 2 liter waterbottles in the engine room for filling the filter fast when it urged, ....changed waterhoses against steelreinforced, several new impellers, and lubricated the filterseal with silicone grease, nothing helped.


This year I changed the place of my vetus waterfilter from 30cm above waterline (mounted originally by HR to this place) first to 15cm above waterline like discribed in the vetus manual. As this did not help I lowered it further to about ~3 cm above waterline. When I look now from top in the open waterfilter I can see the seawater raising in the hose up to 2-3cm below the bottom of the waterfilter. This seems to be enough, since my engine D2-55 is able to suck the water through even when there is no water in the filter.
But still I always listen and check if there is cooling water spouting when ever I start the engine.

Meanwhile I have seen boats which had the waterfilter mounted below waterline and have to close the seacock for cleaning.

I find it saver just above waterline.

[OZ-Sailor]

Just fixed the same problem on d2-55 engine by simply turning the impeller housing face plate around after changing the impeller and found no water pumping.